pH and Temperature Dependence of Low-Core T_g Micellar Structures Formed by PDMAEMA-b-PLMA Diblock Copolymers in Aqueous Solution

A diblock copolymer featuring a hydrophobic block with a low glass transition temperature and a pH-responsive, cationic block is synthesized and investigated with respect to its self-assembly behavior in aqueous solution. The synthesis of the poly(lauryl methacrylate)-block-poly(2-(N,N-dimethylamino) ethyl methacrylate) diblock copolymer PDMAEMA₆₀-b-PLMA₄₀ is carried out using reversible addition fragmentation chain transfer (RAFT) polymerization. Its self-assembly in dilute aqueous solution at pH 7 is investigated using various light scattering methods. Micelles with a positive zeta potential are identified. Synchrotron small-angle X-ray scattering reveals changes in the inner structure of the micelles as a function of temperature and at pH values above, below and close to the pKa value of PDMAEMA (ca. 7.5). At all pH values, cigar-shaped core–shell micelles are found. While the micellar size and shape hardly change with temperature at pH 5, temperature responsivity is observed at pH 7 and 10, resulting in, among others, a change of the core size. These structural changes are facilitated by the softness of the PLMA core. Such systems may be suitable for the co-delivery of hydrophobic drugs and nucleic acids.